The present invention relates to a resin sealed semiconductor device and, particularly, to a resin sealed semiconductor device in which a high integration density semiconductor element can be resin-sealed without changing package size.
A conventional resin sealed semiconductor device is assembled as following manner. For example, a semiconductor element is fixedly secured to a semiconductor element mounting portion of a lead frame made from a thin plate of iron alloy with using silver paste. Then, bonding pads on the semiconductor element are wire-bonded to leads also formed in the lead frame by using wires of metal such as gold or aluminum. Thereafter, the semiconductor element and the lead frame portion therearound are resin-sealed with epoxy resin and portions of the leads extended from the resin sealed portion are separated from the lead frame and are bent.
External dimensions (package size) of the resin sealed semiconductor device assembled in this manner are standardized by JEDEC (Joint of Electron Device Engineering Council) or EIAJ (Electronic Industries Association of Japan). Therefore, for resin sealing of a high integration density semiconductor element having large area, a ratio of a resin sealed portion of the package to the semiconductor element thereof becomes small. As a result, the distance between ends of leads and the semiconductor element becomes small and further the length of suspending leads for supporting the semiconductor element mounting portion also becomes small. Thus, the deep press machining for lowering the level of the semiconductor element mounting portion of the lead frame with respect to the remaining portion thereof becomes difficult.
For this reason, there is a problem that the metal wire for bonding the bonding pads of the semiconductor element to the leads may contact with edge portions of the element, resulting in electric short-circuit.
In order to solve this problem, the so-called LOC (Lead-On-Chip) construction such as shown in U.S. Pat. No. 4,862,245 has been proposed, in which a lead frame does not have a semiconductor component mounting portion and leads are overlapped on a semiconductor component. The leads protruded on the upper surface of the semiconductor elements are directly fixed to the upper surface through insulating adhesive.
To install many bonding pads on a semiconductor element, peripheral sections thereof are useful as bonding pad forming regions. In this case, however, leads (inner leads) pass through the peripheral section between bonding pads. Therefore, in wire-bonding with metal wire, there may be cases that bonding must be done in directions traversing the leads and thus the problem of electric short-circuit between the metal wire and the leads is likely to occur.